The present invention relates to a method of fixing a cutting tip to a pick body to form a cutting pick and to a cutting pick comprising a tip and a pick body which have been fixed together.
Cutting picks are used in a variety of machinery for mechanical rock excavation, such as mining, drilling and other operations, such as surface finishing or levelling for asphalt roads.
Cutting picks usually have a tip at one end thereof, which in use is the part of the pick that engages the surface for cutting purposes, and a body which supports the tip and which is fixed to the cutting machinery. Because the tip is the principal part of the pick which is subject to aggressive loads, it is also the part of the pick which is most likely to wear. Thus, it is desirable that the tip be formed of a material that has optimum characteristics to resist or minimise wear. Because such materials are usually very expensive, cutting picks often are constructed to have a pick body which is formed from one material and a cutting tip which is formed from another. This construction is usually necessitated by economy, such that the pick body, which is the major component by size of the cutting pick, is formed from a much cheaper material than the tip. For example, the pick body is often formed from heat treated steel, whereas the tip can be formed from tungsten carbide. In such constructions, the tip is usually directly fixed to the pick body by brazing. Brazing is not only compatible for bonding between a pick body and tips of these materials, but it also usually provides a sufficient bond to properly fix the pick body to the tip.
Unfortunately, brazing is not suitable for all tip materials. For example, to date it has been found that tips made of diamond composite materials, comprising diamonds which are bonded together in a silicon carbide matrix, otherwise known as silicon carbide diamond-composite (“SiC-D”), are very difficult to properly bond to a steel pick body by normal brazing and soldering techniques. One explanation for this difficulty is that SiC-D has a high carbon content which significantly reduces the ability of braze to bond to the tip. For this reason, there has been a difficulty in making use of SiC-D in cutting picks, even though SiC-D is a material which has particular characteristics that make it very desirable.